The manus of mylodon darwinii Owen (Tardigrada, Mylodontidae) and its phylogenetic implications

ABSTRACT

The first nearly complete and articulated manus of the ground sloth Mylodon darwinii, from the upper Pleistocene of Argentina, is described. It shares similarities with Mylodonopsis ibseni from Brazil, including a cuneiform with a distinct pisiform facet, an obliquely concave ulnar facet, and a prominent distolateral process, as well as a gracile metacarpal III. It shares a flattened pisiform with Glossotherium robustum. The trapezoid is unique in the obliquely elongate proportions of its dorsal surface. Shapes of the articular facets indicate different functions in digits II and III, with the former having a greater range of motion and the latter greater stability at the joints. Clear arboreal or fossorial adaptations are absent. A phylogenetic analysis recovered M. darwinii as closely related to M. ibseni and agrees with larger phylogenetic analyses of sloths based on craniomandibular evidence. Our data support more than two mylodontine dispersal events to North America.

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Citation for this article: Haro, J. A., A. A. Tauber, and J. M. Krapovickas. 2016. The manus of Mylodon darwinii Owen (Tardigrada, Mylodontidae) and its phylogenetic implications. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1188824.

ACKNOWLEDGMENTS

We thank J. Di Ronco for helping A.A.T. with the field work; M. Sosa and A. Montes for preparation work; M. Ramos, C. Yonahara, M. Sosa, and P. Rodríguez for photography; M. Pizarro for 3D scanning; N. Muguiro for access to the 3D scanner in the Laboratorio de Diseño Biomédico (DiBio), Universidad Nacional de Córdoba; H. G. McDonald and two anonymous reviewers for correction of previous versions of this work; H. G. McDonald, Á. Miño-Boilini, G. I. Esteban, C. Cartelle, D. Brandoni, R. Hulbert, K. MacKenzie, J. Bar, M. Dantas, R. Juárez, and N. Gardner for supplying us with relevant literature; the Willi Hennig Society for the free availability of the phylogenetic inference software TNT; and J. Brasca, N. Gardner, H. G. McDonald, J. Welman, and an anonymous reviewer for help with the English style. SeCyT-Universidad Nacional de Córdoba grant 05/I780 to A.A.T. supported this research.